Industrial utilizations of water-soluble sulfuric acid lignin prepared by hydrothermal treatment as flocculant and dispersant

Sulfuric acid lignin (SAL) is a byproduct of the acid saccharification of lignocellulosic materials for bio-fuel generation. The recalcitrant and highly complex structure of SAL significantly limits its industrial use, making it a useless industrial waste. In a previous study, we proposed a hydrothermal reaction for SAL that can convert it into water-soluble compounds (HSALs), which considerably expanded its industrial use scenario. In this study, we converted this water-soluble HSAL into two ionic modifications with applications as flocculants and dispersants. Firstly, the introduction of a carboxy group was carried out with bromoacetic acid. In the carboxymethylated HSAL (C-HSAL), the carboxymethyl groups content was as high as 3.66 mmol/g. Dispersibility tests using gypsum paste showed that C-HSAL exhibited a dispersibility almost equivalent to that of commercial lignosulfonate. Furthermore, another investigation was conducted synthesizing cationized HSAL derivatives by the reaction with glycidyl trimethylammonium chloride (GTA). Dye removal tests were performed with the obtained lignin-based flocculants using three organic dyes. The results showed ideal dye removal ratios for the GTA-HSALs (higher than 90% for all dyes tested), thereby suggesting that they have a huge potential as core molecules to develop high-efficient dye flocculants.